1. Field of the Invention
The present invention is broadly concerned with dispenser devices and methods for precisely dispensing viscous, flowable materials. More particularly, the invention pertains to embodiments of such inventions and methods wherein accurate quantities of material can be repeatedly dispensed while minimizing the possibility of air drying of the material adjacent the dispenser outlet. In preferred practice the dispensers of the invention include a deformable outlet tube with a flow controlling assembly comprising a tube-engaging element (e.g., a roller) supported by an actuator linkage so as to selectively move the element to deform the outlet tube with continued movement of the element serving to generate a suction force adjacent the tube outlet end so that the flowable material at the end is drawn into the confines of the tube.
2. Description of the Prior Art
In the manufacture of integrated circuits, materials such as photo sensitive resins (photoresists) are applied to wafers, and the wafers are spun to evenly distribute the materials. Most photoresists and related materials are extremely expensive, and therefore care must be taken to use only the minimum amount of the composition necessary to accomplish the desired end. In practice, computer controlled syringe-type dispensers have been used to dispense materials of this character. These dispensers include a replaceable syringe supported on an actuator housing, with the syringe including a material reservoir and an elongated deformable outlet tube. Various types of controllers are used to selectively pinch off the outlet tube to terminate material flow from the syringe.
For example, U.S. Pat. Nos. 4,030,640, 3,982,724 and 5,033,656 describe various dispensers which include pinch-type flow controllers. The ""724 patent makes use of a micrometer stop which is used to pinch off a deformable outlet tube. Similarly, the ""640 patent employs a conical pinch element for this purpose. The ""656 patent makes use of a pair of pinch elements.
However, the viscous nature of many materials, and particularly those used in the electronics industry, often cause a terminal droplet to form at the outlet end of material dispensing tubes. As a consequence, the material may dry at the end of the tube, requiring cleaning which can waste the materials, thus making simple pinch-type dispensers unsuitable.
In addition, commercial systems are available which use a mechanical apparatus to control the plunger of delivery syringes. However, these devices are large and somewhat expensive, and generally require the use of additional fluid tubing to connect the dispenser apparatus to the point where fluid is to be dispensed. This can be a problem if dispensing operations are interrupted or terminated for significant periods of time, in that the material may tend to dry within the tubing. In addition, this causes extra waste of materials in that the additional fluid tubing and associated fittings must be filled with fluid before use.
Pneumatic point-of-use syringe systems also exist that employ various methods of control of the pressure or vacuum in the syringe barrel to control the dispensing cycle. When used with materials that flow (as opposed to pastes) the materials are prevented from dripping by the application of a vacuum to the upper part of the syringe barrel. The level of vacuum must be high enough to prevent dripping yet not high enough to pull air through the dispenser tip and into the syringe barrel. Unfortunately, the level of vacuum required varies with the characteristics of the fluid and dispenser tip, as well as the amount of fluid remaining in the syringe barrel.
The present invention provides an improved dispenser for viscous flowable materials of compact, simplified design which overcomes many of the problems with prior art dispensers. To this end, the dispensers of the invention include a reservoir for holding materials to be dispensed, with a deformable outlet tube coupled with the reservoir and presenting an outlet end. A flow controlling assembly including a tube-engaging pinch element and an actuator are used to selectively move the element between a flow-permitting position adjacent the tube and a flow-blocking, tube-deforming engagement with the tube. To this end, the pinch element operates against an opposed backing surface, i.e., the outlet tube is disposed between the pinch element and backing surface. Furthermore, and very importantly, the element is moved by the actuator along the tube in a direction away from the outlet end in order to create a suction which draws material at the outlet end into the tube. This effectively eliminates problems associated with dripping and/or drying of material at the outlet end of the tube.
In preferred forms, the dispenser of the invention includes a small, upright housing adapted to receive a standard, removable dispenser syringe. The housing is configured to accept the syringe body with the filtered depending syringe outlet tube extending below the housing. A flow controlling assembly is located within the housing and includes a roller or similar tube-engaging element together with an actuary linkage assembly which may be pneumatically or mechanically operated. Advantageously, the roller is moved through an arcuate path to first engage the outlet tube and then moved upwardly along the length thereof to create the desirable suction at the end of the outlet tube. In order to achieve the best and most accurate flow control, the pinch closure effected between the pinch element and backing surface is resilient and biased. Such maybe obtained by a resilient bias associated with either the pinch element or the backing surface.
In further preferred forms, the dispenser has a bypass assembly which terminates delivery of pressurized air to the dispenser syringe, thereby preventing inadvertent dispensing of material. Additionally, a flow control valve may be provided which includes a selectively adjustable metering valve allowing the user to adjust the speed of operation of the flow-controlling assembly during movement thereof from the flow-permitting to the flow-blocking position thereof.